For prevention and cure of AIDS, it is important to know the mechanism of how cell lineage for T lymphocyte is determined during embryonic development. T lymphocytes are derived from hematopoietic stem cells, however, it is still unclear how hematopoietic cells are developed from undifferentiated mesodermal tissues. We are focusing on the function of Bone Morphogenetic Proteins (BMPs), the members of TGF-beta superfamily, during mouse development. BMPs have function to specify the fate of mesodermal tissues more ventral. Hematopoietic cells are derived from the most ventral mesoderm, therefore, BMPs are hypothesized to play important roles during specification of T lymphocyte lineage in the hematopietic tissues. To reveal the function of BMP signaling during hematopoiesis, we will set up hematopoietic cell specific disruption of BMP receptor genes using embryonic stem cell technology. The knowledge that will be acquired through this research may give us better understanding for etilogy of AIDS and hopefully for prevention and cure of this fatal disease. - AIDS, ES cells embryo culture tissue specific knock-out